What If We Got Sunlight All Wrong? The Truth About Vitamin D & Chronic Disease

Mark Hyman

Jul 14, 2025

Episode description

Sunlight has long been vilified for its link to skin cancer, yet hiding from it entirely may be costing us far more. Vitamin D, made primarily through sun exposure, plays a pivotal role in everything from bone strength and immune defense to mood regulation, cancer prevention, and even longevity. Shockingly, over 80% of people have levels too low to unlock its protective powers—putting them at greater risk for chronic illness, and even premature death. Research shows that raising vitamin D to optimal levels could prevent hundreds of thousands of deaths each year, rivaling or surpassing the impact of many medical interventions. With a few minutes of daily sun, the right kind of supplementation, and awareness of how our lifestyles block this essential nutrient, reclaiming our health may be simpler than we think.

In this episode, I discuss, along with Dr. Cindy Geyer, the critical role of vitamin D in preventing chronic disease, boosting immunity, and promoting overall health.

Dr. Cindy Geyer received her bachelor of science and her doctor of medicine degrees, with honors, from the Ohio State University. She completed residency in internal medicine at Strong Memorial Hospital in Rochester, N.Y. and is triple board certified in internal medicine, integrative medicine and lifestyle medicine.

This episode is brought to you by BIOptimizers.

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Full-length episodes can be found here:

Do You Need To Take Vitamin D?Choosing Skin Care Products that Won’t Make You Sick Why Boosting Your Vitamin D Could Change Your Life

Mindsip insights from this episode:

Understand melanoma's risk beyond sun exposure

Unlike basal and squamous cell cancers, the deadly skin cancer melanoma is not as strongly linked to sun exposure and can occur in non-sun-exposed areas.

#cancer

#skin

Maintain vitamin D levels above 50 ng/mL to eliminate COVID death risk

An Israeli study found that if your vitamin D level was over 50 ng/mL, your risk of death from COVID was zero.

#COVID-19

#vitamin-D

Avoid sunscreens with vitamin A to reduce skin cancer risk

You should be particularly careful with sunscreens containing vitamin A, as it can paradoxically make skin cancer more likely.

#cancer

#sunscreen

Perform simple self-test for vitamin D deficiency

You can perform a simple self-test for vitamin D deficiency by pushing your thumb hard on your shin; if it hurts, you are likely deficient.

#deficiency

#vitamin-D

Address chronic nutrient deficiencies to prevent long latency diseases

Chronic, low-level nutrient deficiencies can lead to "long latency deficiency diseases" like osteoporosis and cancer over many years.

#cancer

#deficiency

Maintain vitamin D levels above 60 ng/mL to lower breast cancer risk

Women with vitamin D levels over 60 ng/mL had an 82% lower risk of breast cancer compared to those with levels under 20 ng/mL.

#breast-cancer

#vitamin-D

Boost vitamin D levels as aging reduces skin production

The average 70-year-old's skin creates only 25% of the vitamin D from sun exposure that a 20-year-old's does.

#aging

#vitamin-D

Aim for optimal vitamin D levels above 45 ng/mL

Standard lab reference ranges for vitamin D reflect a deficient population, whereas the optimal level for health should be over 45 or 50 ng/mL.

#testing

#vitamin-D

Mark Hyman

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